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## Tracking Items Over Time

Hello everyone,

I am wondering about the best way to handle migration of items in a population. For example, let's say in period 1 I have items A, B, and C. Then in period 2 I have items B, C, and D. Let's say I'm summing some value associated with the items:

Period, Item, Value

1, A, 20

1, B, 40

1, C, 50

2, B, 45

2, C, 52

2, D, 61

];

And I want to decompose the change in Value across:

1)     Items dropped in period 2

2)     New items in period 2

3)     Common items between periods

What I have done so far is to use a calculated dimension:

If(SubstringCount(Aggr(Concat(Distinct [Item #] & Period & '|'),[Item #]),[Item #])&Max(Period)&'|'

,If(SubstringCount(Aggr(Concat(Distinct [Item #] & Period & '|'),[Item #]),[Item #])&Min(Period)&'|'

,'Common Item'

,'New Item')

,'Dropped Item')

This works but is very processor intensive. What has everyone else done to solve this problem? I have roughly 2 million unique items across my periods. I was thinking of adding a new dimension that has all the possibilities, like this:

A, In Period 1 not in Period 2

B, In Period 1 and Period 2

C, In Period 1 and Period 2

D, In Period 2 not in Period 1

I'm afraid this will produce many millions of rows, but may be faster than my calculated dimension.

Any ideas?

1 Solution

Accepted Solutions
MVP

for 2 period, I think you can count

source:

Period, Item, Value

1, A, 20

1, B, 40

1, C, 50

2, B, 45

2, C, 52

2, D, 61

];

Item, count(Item) as cnt

Resident source

group by Item;

if(cnt=2, '1 and 2', 'only ' & Period) as NewDim

Resident source;

2 Replies
MVP

for 2 period, I think you can count

source:

Period, Item, Value

1, A, 20

1, B, 40

1, C, 50

2, B, 45

2, C, 52

2, D, 61

];

Item, count(Item) as cnt

Resident source

group by Item;

if(cnt=2, '1 and 2', 'only ' & Period) as NewDim

Resident source;

Not applicable
Author

Hi Massimo,

That is a great idea. You've inspired me to look at multiple periods:

ItemMigrationDim:

NoConcatenate

source:

Period, Item, Value

1, A, 20

1, B, 40

1, C, 50

2, B, 45

2, C, 52

2, D, 61

3, A, 15

3, C, 20

3, D, 18

3, E, 85

];

NoConcatenate

PeriodsTemp:

NoConcatenate

Periods:

LOAD Period Resident PeriodsTemp Order by Period;

drop table PeriodsTemp;

FOR i = 0 to NoOfRows('Periods') - 1

Let vBasePeriod = Peek('Period',i,'Periods');

FOR j = i + 1 to NoOfRows('Periods') - 1

Let vComparisonPeriod = Peek('Period',j,'Periods');

Temp:

LOAD Item, Min(Period) as MinPeriod, Max(Period) as MaxPeriod Resident source Where Period = \$(vBasePeriod) or Period = \$(vComparisonPeriod) Group By Item;

Concatenate(ItemMigrationDim)

,If(MinPeriod = \$(vComparisonPeriod),\$(vComparisonPeriod) & ' not ' & \$(vBasePeriod)

,If(MaxPeriod = \$(vBasePeriod), \$(vBasePeriod) & ' not ' & \$(vComparisonPeriod),\$(vBasePeriod) & ' and ' & \$(vComparisonPeriod)

)

) as MigrationText

,\$(vBasePeriod) as BasePeriod

,\$(vComparisonPeriod) as ComparisonPeriod

Resident Temp;

drop table Temp;

NEXT

NEXT

DROP Table Periods;

For some reason when I took the distinct on Period it was never in order. I tried adding Order By Period, but it still didn't work, so I had to put it in a temp table.

I made a straight table with this expression:

=Sum({<BasePeriod = {\$(=Min(Period))}, ComparisonPeriod = {\$(=Max(Period))}>} Value)

That way only the relevant periods show up in the table.

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